Post hole diggers mounted on a three-point hitch of a tractor and connected to the tractor power takeoff are highly effective in digging post holes, but inclusion of a mechanism to reverse rotation of the auger is needed in case underground obstacles such as strong roots or rocks are encountered. Various approaches have been taken, including use of a kit or adapter including a gear transmission providing forward and reverse capability, with this mechanism being placed outside of the power head of the system. It is desired to include a reversing mechanism within the power head, with this mechanism being self-contained in a common housing or case, so that such capability is provided for in initial design and manufacturing steps.